Fluidic switching circuits

ABSTRACT

The invention relates to a fluidic pressure-ratio switching system, which gives an output pressure signal when one control pressure is higher than another in which the output pressure is a high of an input pressure which is used to drive the system. A fluidic bistable device performs the switching function and a fluidic proportional amplifier provides the pressure recovery, the outputs of the bistable device being used to provide control pressures for the proportional amplifier. A flow restrictor is connected in one output of the bistable device and a further flow restrictor is connected between the proportional amplifier control connections. A predetermined pressure ratio therefore exists between these control connections. In order to prevent feedback of pressure from the proportional amplifier to the bistable device a further bistable device may be connected in each line between the switching bistable and the amplifier. Alternatively, a monostable device may be connected in one of the lines and the other of the lines exhausted to atmosphere.

United States Patent [72] Inventor Ronald Alfred Heath l-larborne, Birmingham, England [21] Appl. No. 860,165 [22] Filed Sept. 17, 1969 [45] Patented Oct. 19, 1971 [73] Assignee Joseph Lucas (Industries) Limited Birmingham, England [32] Priority Sept. 30, 1968 [33] Great Britain [31] 46264/68 [54] FLUIDIC SWITCHING CIRCUITS 13 Claims, 3 Drawing Figs.

[52] US. Cl l37/81.5, 235/201 [51] lnt.Cl F15c 1/12 [50] Field ofSearch .137/81.5; 23 5/201 200 [5 6] References Cited UNITED STATES PATENTS 3,338,515 8/1967 Dexter 137/8l.5 X 3,399,829 9/1968 Richards et a1. 137/8 1 .5 X 3,409,032 11/1968 Boothe et a1 137/81.5 X 3,420,255 1/1969 Wilkerson 137/81.5

Primary Examiner-Samuel Scott Atl0rney1-lolman & Stern ABSTRACT: The invention relates to a fluidic pressure-ratio switching system, which gives an output pressure signal when one control pressure is higher than another in which the output pressure is a high of an input pressure which is used to drive the system. A fluidic bistable device performs the switching function and a fluidic proportional amplifier provides the pressure recovery, the outputs of the bistable device being used to provide control pressures for the proportional amplifier. A flow restrictor is connected in one output of the bistable device and a further flow restrictor is connected between the proportional amplifier control connections. A predetermined pressure ratio therefore exists between these control connections. In order to prevent feedback of pressure from the proportional amplifier to the bistable device a further bistable device may be connected in each line between the switching bistable and the amplifier. Alternatively, a monostable device may be connected in one of the lines and the other of the lines exhausted to atmosphere.

FLUIDIC SWITCHING CIRCUITS This invention relates to fluidic switching circuits and has an object to provide a switching circuit in a convenient form.

A fluidic switching circuit in accordance with the invention comprises essentially a bistable fluidic device having an inlet port, a pair of outlet ports and a pair of control ports arranged so that when the pressure at one of the control ports is higher than the pressure at the other control port there is a pressure output from one of the outlet ports, and when the pressure at said other control port is higher than the pressure at said one control port there is a pressure output from the other outlet port, a fluidic proportional amplifier device having an inlet port, a pair of outlet ports, and a pair of control ports such that the pressures at said outlet ports are continuously variable as a function of the pressures at said control ports, said control ports of the proportional amplifier being connected so as to receive control pressure signals derived from the outlet ports of the bistable device, and a pair of flow restrictors one of which connects one of the control ports of the proportional amplifier device to one of the said control pressure signals and the other of which interconnects the control ports of the proportional amplifier device so as to establish a predetermined pressure ratio between said control ports when the bistable device is in one of its stable states.

The accompanying drawings are fluidic circuit diagrams illustrating three examples of the present invention.

In the example shown in FIG. 1 the circuit makes use of two different fluidic devices. Firstly there is a device which is a bistable device operating on the Coanda effect. This device has an inlet port 11, a pairof outlet ports 12, 13, and a pair of control ports 14, the arrangement is such that when pressure P is applied to the inlet port 11 and the pressure P, at port 14 is higher than pressure P at port 15, the pressure at port 12 will be approximately zero and the pressure at port 13 will be a proportion of the full inlet pressure P. The proportion is usually about one third, but varies with the actual geometry of the device. When the pressure P, exceeds the pressure I the high pressure will be delivered from the port 12. The flow state of the device 10 changes rapidly as P rises above or falls below P The other device 16 is a so-called proportional amplifier and has, asbefore an inlet port 17, two outlet ports 18, 19 and two control ports 20, 21. In this device the Coanda effect does not occur and the device operates simply by the deflection of a jet from the inlet port 17 towards either of the ports 18, or 19 by signals applied to the ports 20, 21. When the pressure at ports and 21 are equal the pressures at ports 18 and 19 will be substantially equal and the pressure at port 18 will rise as the pressure at port 21 rises. The pressure at port 19 will rise if the pressure at port 21 falls whilst the pressure at port 20 remains constant.

With such a device the maximum pressure I at the port 18 will be obtained when the ratio of the pressures at ports 20 and 21 is at a predetermined value which is substantially independent of the pressure at the inlet port 17.

As shown in FIG. 1 the inlet 11, 17 of the two devices are connected to a common pressure supply P, port 12 of device 10 is connected via a restrictor 22 to port 20 of device 16 and port 13 of device 10 is connected to port 21 of device 16. A

second restrictor 23 interconnects the ports 20, 21 of the device 16. The arrangement is such that when the pressure P is less than the pressure P, there will be no pressure signal applied to the port 21 of the device 16 although a signal will be applied to the port 20. The pressure P delivered from port 18 of the device 16 will therefore be a minimum. When the pressure P, rises above the pressure P, the device 10 will assume its other stable state so that pressure will be applied to port 21 of device 16. At the same time a pressure will be generated at port 20 as a result of flow through the orifices 23, 22 in series exhausting through device 10. The flow restrictors 23, 22 are adjusted to ensure that the ratio of the pressures at ports 21 and 20 are such as to give optimum recovery in port 18 so that as P, rises above P, there will be a sudden change in the pressure P,,

The circuit shown in FIG. 1 is extremely stable and can be used in controls where high hysteresis can be tolerated. Such hysteresis arises because of the inevitable feedback of pressure signals from the device 16 to the device 10.

Turning now to the circuit shown in FIG. 2 the circuit is exactly as described in FIG. 1 except that a pair of additional bistable devices 24, 25 have been included in the connections between the ports 12 and 13 of the device 10 and the ports 20 and 21 of the device 16 respectively. Each bistable device 24, 25 is biased to one of its two stable states by means of a connection between its inlet port and one of its control ports via restrictors 26, 27 respectively. The device 24 has its other control port connected to port 12 and device 25 has its other control port connected to port 13 of the device 10, such that a pressure signal from port 12 will cause the device 24 to be switched from the stable state to which it is biased so that pressure is delivered via the restrictor 22 to the port 20 of the device 16, and, similarly, when pressure is delivered from port 13 of device 10 device 25 causes pressure to be delivered to port 21 of the device 16. The bistable devices 24 and 25 prevent feedback from the device 16 to device 10 and thereby reduce the high hysteresis effect inherent in the circuit shown in FIG. 1.

In FIG. 3 a single monostable device 28 has been employed instead of the two bistable devices 24, 25. This device 28 has an inlet port 29, a pair of outlet ports 30 and 31 and a control port 32. The device is such that when there is no pressure signal applied to the control port 32 there is a pressure signal at the outlet port 30, but this disappears when pressure is ap plied at port 32 and a pressure signal appears at port 31 in stead.

In the arrangement shown in FIG. 3 the port 12 of the bistable device is vented to atmosphere whilst port 13 is connected to the control port 32 of the monostable device 28. Port 30 of the bistable device 28 is connected via the restrictor 22 to port 20 of the device 16 whereas port 31 of the monostable device 28 is connected directly to the control port 21 of device 16. Once again feedback from the device 16 to the device 10 is prevented, whilst high-pressure recovery is obtained in the device 16 by the virtue of the control of the pressures at ports 21 and 20 by the flow restrictors 23, 22 when the pressure P, exceeds the pressure P It is to be noted that the ambient pressure around each fluidic device in each case may be maintained at a level other than the existing atmospheric pressure. This can result in better switching of the bistable devices with the result that higher pressures are passed from the outlet ports to the control ports of the devices in the following stage or stages.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

l. A fluidic switching circuit comprising a first bistable fluidic device having an inlet port, a pair of outlet ports and a pair of control ports arranged so that when the pressure at one of the control ports is higher than the pressure at the other control port there is a pressure output from one of the outlet ports, and when the pressure at said other control port is higher than the pressure at said one control port there is a pressure output from the other outlet port, a fluidic proportional amplifier device having an inlet port, a pair of outlet ports, and a pair of control ports such that the pressures at said outlet ports are continuously variable as a function of the pressures at said control ports, said control ports of the proportional amplifier being connected so as to receive control pressure signals respectively derived from the outlet ports of the bistable device, and a pair of flow restrictors one of which connects one of the control ports of the proportional amplifier device to one of the said control pressure signals and the other of which interconnects the control ports of the proportional amplifier device so as to establish a predetermined pressure ratio between said control ports when the bistable device is in one of its stable states.

2. A circuit as claimed in claim 1 in which the inlet ports of the bistable device and the proportional amplifier device are connected to a common supply pressure.

3. A circuit as claimed in claim 1 in which the fluid pressure at one of the outlet ports of the proportional amplifier device constitutes an output signal of the circuit.

4. A circuit as claimed in claim3 in which the other of the outlet ports of the proportional amplifier device is connected to atmosphere.

5. A circuit as claimed in claim 3 in which the said predetermined pressure ratio is such as to cause the pressure at the said one outlet port of the proportional amplifier for any given pressure at the inlet port thereof to be a maximum.

6. A circuit as claimed in claim 1 which includes a further pair of bistable fluidic devices, substantially identical to the said first mentioned bistable device, each having a control,

are all connected to a common supply pressure.

9. A circuit as claimed in claim 6 which includes biasing means for each said further bistable device so that, in the absence of a pressure signal from an associated outlet port of the first-mentioned bistable device, no pressure signal is supplied by the said further bistable device to a corresponding control port of the proportional amplifier device.

10. A circuit as claimed in claim 9 in which the said biasing means is a pressure signal derived from the supply pressure and applied to a control port of each said further bistable device. I

11. A circuit as claimed in claim 1 which includes a monostable fluidic device having an inlet port, a control port connected to one output of the bistable device and a pair of outlet ports each providing a respective one of the control pressure signals to the proportional amplifier device.

12. A circuit as claimed in claim 11 in which the inlet ports of the monostable device, the bistable device and the proportional amplifier device are all connected to a common supply pressure.

13. A circuit as claimed in claim 11 in which one outlet of the first bistable device is connected to atmosphere. 

1. A fluidic switching circuit comprising a first bistable fluidic device having an inlet port, a pair of outlet ports and a pair of control ports arranged so that when the pressure at one of the control ports is higher than the pressure at the other control port there is a pressure output from one of the outlet ports, and when the pressure at said other control port is higher than the pressure at said one control port there is a pressure output from the other outlet port, a fluidic proportional amplifier device having an inlet port, a pair of outlet ports, and a pair of control ports such that the pressures at said outlet ports are continuously variable as a function of the pressures at said control ports, said control ports of the proportional amplifier being connected so as to receive control pressure signals respectively derived from the outlet ports of the bistable device, and a pair of flow restrictors one of which connects one of the control ports of the proportional amplifier device to one of the said control pressure signals and the other of which interconnects the control ports of the proportional amplifier device so as to establish a predetermined pressure ratio between said control ports when the bistable device is in one of its stable states.
 2. A circuit as claimed in claim 1 in which the inlet ports of the bistable device and the proportional amplifier device are connected to a common supply pressure.
 3. A circuit as claimed in claim 1 in which the fluid pressure at one of the outlet ports of the proportional amplifier device constitutes an output signal of the circuit.
 4. A circuit as claimed in claim 3 in which the other of the outlet ports of the proportional amplifier device is connected to atmosphere.
 5. A circuit as claimed in claim 3 in which the said predetermined pressure ratio is such as to cause the pressure at the said one outlet port of the proportional amplifier for any given pressure at the inlet port thereof to be a maximum.
 6. A circuit as claimed in claim 1 which includes a further pair of bistable fluidic devices, substantially identical to the said first mentioned bistable device, each having a control port connected to a respective one of the outlet ports of the first mentioned bistable device and an outlet port providing a respective one of the control signals to the proportional amplifier.
 7. A circuit as claimed in claim 6 in which one of the outlet ports of each said further bistable device is connected to atmosphere.
 8. A circuit as claimed in claim 6 in which the inlet ports of the said further pair of bistable devices, the said first mentioned bistable device and the proportional amplifier device are all connected to a common supply pressure.
 9. A circuit as claimed in claim 6 which includes biasing means for each said further bistable device so that, in the absence of a pressure signal from an associated outlet port of the first-mentioned bistable device, no pressure signal is supplied by the said further bistable device to a corresponding control port of the proportional amplifier device.
 10. A circuit as claimed in claim 9 in which the said biasing means is a pressure signal derived from the supply pressure and applied to a control port of each said further bistable device.
 11. A circuit as claimed in claim 1 which includes a monostable fluidic device having an inlet port, a control port connected to one output of the bistable device and a pair of outlet ports each providing a respective one of the control pressure signals to the proportional amplifier device.
 12. A circuit as claimed in claim 11 in which the inlet ports of the monostable device, the bistable device and the proportional amplifier device are all connected to a common supply pressure.
 13. A circuit as claimed in claim 11 in which one outlet of the first bistable device is connected to atmosphere. 